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Bug #16351

Updated by nobu (Nobuyoshi Nakada) about 5 years ago

Hello, while working on improving memory allocations in one of my apps, I stumbled upon the following behavior. I measured three different ways of passing variables to a new `Object`, Object, using plain params, using a hash and using keyword arguments. 

 ```ruby ``` 
 class FooWithPlainParams 
   def initialize(a, b, c) 
     @a = a 
     @b = b 
     @c = c 
   end 
 end 

 class FooWithOptionsHash 
   def initialize(options = {}) 
     @a = options[:a] 
     @b = options[:b] 
     @c = options[:c] 
   end 
 end 

 class FooWithKeyword 
   def initialize(a:, b:, c:) 
     @a = a 
     @b = b 
     @c = c 
   end 
 end 
 ``` 

 I used memory_profiler gem to measure the allocations with the attached script, calling new 100 times, using ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin19] 

 `FooWithPlainParams` FooWithPlainParams not surprisingly just reported "Total allocated: 4000 bytes (100 objects)". 
 `FooWithOptionsHash` FooWithOptionsHash reported "Total allocated: 27200 bytes (200 objects)" with 100 `Hash` Hash allocations. This makes sense, since the params are passed on as a `Hash`. Hash. 
 `FooWithKeywordArguments` FooWithKeywordArguments reported "Total allocated: 50400 bytes (300 objects)" with 200 `Hash` Hash allocations, which is a bit surprising. 

 After that I checked out ruby-head and there `FooWithKeywordArguments.new` FooWithKeywordArguments.new reports only 100 `Hash` Hash allocations as `FooWithOptionsHash`. FooWithOptionsHash. So that part seems to be fixed. 

 What surprised me so was, that using the same way of passing parameters in another method, resulted in no allocated Hash according to memory_profiler gem. 

 ```ruby ``` 
 class FooWithKeyword 
   def foo(d:, e:, f:) 
     @d = d; @e = e; @f = f 
   end 
 end 
 ``` 

 Calling `foo(d: 4, e: 5, f: 6)` on a `FooWithKeyword` FooWithKeyword object, does not show any allocations. 

 What is the difference here between `foo` and `initialize`?

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